grondahl



Juiy 29. 1924.

' L. O. GRONDAHL RAILWAY SIGNALING Original Filed April 16 1.921 4 Sheets-Sheet 1 INVEETOR: (Q, fifwoLo-ia,

m ATTORNEY.

L. O. GRONDAHL July 29 19-24.

RAILWAY SIGNALING H mm m .r i n u Original Filed April 15 N g- Q. way-Me,

A145, ATTORNEY.

July 29 1924. 1,503,318

L. o. G RONDAHL RAILWAY S IGNALING Original Fil d April 16 1921 4 Sheets-5heet 3 LJ TA 78 7,6 7,7 L-"J E LP? 5 so, n fi r I L-I l Fig: 7.

INVENTOR.

#L' BY A L ATTORNEY.

July 29 1924. 1,503,318

L. o. GRONDAHL RAILWAY s IGNALklNG Original Filed April is. 1921 4 Sheets-Sheet 4 INIZENTOR.

H4 A'I'TORNEY.

Patented July 29, 1924.

LABS O. GBONDAHL, 0F PITTSBURGH, PENNSYLVANIA, ASSIGNOR TO THE UNION SWITCH & SIGNAL'COMPANY, OF SWISSVALE, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

RAILWAY SIGNALING.

Application filed April 16, 1921, Serial No. 461,782. Renewed May 20, 1924.

T 0 all whom it may concern:

Be it knownthat I, ELARS O. GRONDAHL, a citizen of the United States, residing at Pittsburgh, in the county of Allegheny and State of Pennsylvania, have invented certain new and useful Improvements in Railway Signaling, "of whichthe following is a specification. s

' My invention relates to railway signaling, and is particularly well adapted to signaling of the typewherein roadside signals are controlled by track circuits.

I will describe several forms of signaling apparatus embodying my invention, and will then point out-the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing one form of signaling apparatus embodying my invention. Figs. 2, 3 and 4 are views showing modifications of the system shown in Fig. 1; Fig. 5 is a fragmental view similar to a por-' tion of Fig. 4 but showing diagrammatically an induction motor type of electro-re sponsive device which may be substituted for the dynamometer device illustrated in Figs. 1 to 4: inclusive. Fig. 6 is a view showing in section a dynamometer type of electro-responsive device together with one arrangement of the mirrors and light-responsive cells associated therewith. Fig. 7 is a view similar to .Fig. 6 butshowing a modified. means for mounting the moving parts of the device. Fig. 8 is a view similar to Fig. 6 but showing the induction-motor type of electro-responsive device illustrated diagrammatically in Fig. 5. Fig. 9 is a ver tical sectional view taken on the'linc IX'IX' of Fig. 8.

Similar reference characters refer to similar parts in each of the several-views.

Referring first to Fig. 1, the reference characters 2 and 2 designate the track rails of a railway along which traflic normally moves from right to left, as indicated by the arrow, and which rails :are divided by insulated'joiiit's i l to form a series of track sections AB, B-G,.etc. 7

Each section is provided With-a track circuit comprising a source of current'and an electro-responsive device, the former being connected across the rails at the exit end of the section and the latter receivi g current from the rails at the entrance'end of the section. As here shown, the source of current for each section is the secondary 4: of a transformerwhich is disignated T with an exponent corresponding to the location. This secondary is connected across the rails by Wires 47 and 48, the connection 48 including the primary of a transformer designated F with an exponent corresponding to the location,'and the function of which is explained hereinafter. The primary 5 of each transformer T is connected with transmission mains 6 to which alternating signaling current is constantly supplied by a generator 7.

The electro-responsive device for each sec tion is designated by the reference character E, with an exponent corresponding to the location. As here shown this device is a. suspended coil galvanometer, having fixed field coils 8 and 8 and a movable armature comprising a pair of coils 9 and 10. The two field coils are connected in. series across thetraclr rails at the entrance end of the'section, and. one of the armature coils 9 is also connected across the rails at the same point. The other armature coil 10 is connected with the secondary of the transformer F at the second location in advance. The armature is-biase'd to an intermediate position (see device E), but can be moved to a left-hand extreme position (see device E or to a right-hand extreme position (see device E The coils 9 and 10 are so wound and connected thatthe coil 9 tends to swing the armature to the left and the coil 10 tends to swing it to the right. Considering the device 'E for example, when both track sections AB, and B-C are unoccupied the torque due to coil 9 is stronger than the torque due to coil 10, so that the armature is swung to theleft-hand extreme position. When track section AB is occupied, l1ow ever, the current drawn from the secondary 4 of transformer T is considerably increased, so that the current supplied to coil 10 of the electro-responsive device E from the transformer F is also considerably in creased. The torque due to coil 10 is then stronger than that due to coil 9, so that the armature is swung to the right-hand extreme position. When track section B-C is occupied by a car or train, the field coils 8 and 8 of the electro-responsive device E as 1 well as the armature coil 9 will be deprived of current, so that the armature of this device will assume its intermediate position.

Located at the entrance end of each track section are a source of light 12 and three light-responsive cells 18 13 and 13 The source of light 12, which will usually be an electric incandescent lamp, is constantly lighted, and as here shown, is supplied with current from a secondary 14- on the adjacent transformer T through a circuit which will be obvious from the drawing. Each lightresponsive cell 13 has the characteristic of varying in electrical resistance in accordance with variations in the intensity of the light to which it is exposed. It may comprise a substance, such as selenium, stibnite or copper oxide, or it may be what is known asa photo-electric cell in which the active material is usually an alkali metal. The precise nature and form of these cells do not constitute any part of my present invention. Attached to the armature of each electroresponsive device E is a mirror 11 which is arranged to reflect a beam oflight from the adjacent lamp 12 to the adjacent light-re sponsive cells 13 13 and 13*. When the armature is in the intermediate position, the mirror 11 reflects a beam of light from the lamp 12 to the lightresponsive cell 13 lVhen the armature moves to the left-hand extreme position, the mirror reflects a beam of light upon the cell 13 and when it moves to the V right-hand extreme position the mirror refleets a beam of light upon the light-responsive cell 13 The operation of the electro-responsive device E can best be explained by reference to one of these devices, such as E l/Vhen both of the sections BG and A-B are unoccupied,the coil 9 of the electro-responsive device E receives a considerable amount of current from the rails of section BC, so

that the armature of this device is then swung to the left-hand extreme position wherein the light-responsive cell l3 is illuminated. When section AB is occupied, the current flowing in the transformer F is increased in value to such an extent that the effect of coil 10 in the device E overbalances the eflect of coil 9, whereupon the shown, comprises three electric lamps G, Y and R, which lamps when lighted indicate proceed, caution and stop, respectively. Referring to signal S the circuit for the proceed lamp G is from the secondary 15 of transformer T through wires 16, 17 and 18, lamp Gr, light-responsive cell 13, and wire 21 to the secondary 15. The circuit for the caution lamp Y is from secondary 15, through wires 16 and 20, lamp Y, cell 13 and wire 21 to the secondary 15. The circuit for the red lamp R is from the secondary 15, through wires 16, 17 and 19, lamp R, light-responsive cell 13 and wire 21 to the secondary 15.

It will be seen, therefore, that the three lamps of each signal are connected in multiple across the terminals of the secondary 15 of the adjacent transformer T, and that one of the light-responsive cells 13 is included in series with each lamp. The lamps and the light-responsive cells are so proportioned that when any one of the light-responsive cells is illuminated by a beam from the lamp 12, the signal lamp which is in series with such cell will be lighted but the other signal lamps will be extinguished. This result is due to the fact that the electrical resistance of each cell 13 is considerably lower when the cell is illuminated than when it is not. In order to obtain the proper current values it may be found advantageous to interpose a transformer between each light responsive cell and the corresponding lamp. 7

In the actual practice of my invention each light-responsive cell 13 will be pro tected in a suitable manner so that the only rays of light which may reach the active material or substance of such cell are the rays which are projected by the mirror 11 position because of the fact that the influence of coil 10 overbalances that of coil 9, so that light responsive cell 13 at point C is illuminated, with the result that lamp Y of signal S is lighted and this signal indicates caution; At the point D the armature of the electro-responsive device E is swung to the left-hand extreme position, so that light-responsive cell 13 is ilhuninated with the result that lamp G of signal S is lighted and this signal indicates proceed.

When the train 1V passes out of track section AB it will be obvious that signal S will change-to caution and signal S will change to proceed.

Referring now to Fig. 2, the electro-responsive devices are controlled in the same manner as in Fig. 1, with the exception of the armature coil 10, the circuit for which will be explained hereinafter. The mirror 11 performs the same functions as in Fig. 1 except that when the armature of the electro-responsive device occupies its intermediate position this mirror does not reflect light upon any light-responsive cell.

Considering signal S the circuit for the stop lamp R is fromthe middle point of secondary 15 of transformer T through wires 29 and 30, lamp R, resistance 31 and resistance 32 to the left-hand terminal of secondary 15. The circuit for the proceed lamp G is from the right-hand terminal of secondary 15, through resistance 33, wires 34, 35 and 36, light-responsive cell 13 lamp G, wire 39, and resistance 32 to the lefthand terminal of secondary 15. The cantion lamp Y receives energy from transformer T at location B, an the circuit for this lamp passes from the right-hand terminal of the secondary 15 of transformer T through resistance 33, wire 42, resistance 42*, wires 42 43, lamp Y, wires 4 1, 4:5 and 29 to the middle point of secondary 15. The light-responsive cell 133' is included in a shunt around cell 13 and lamp G, which shunt passes from wire 35, through cell 13 and wire 41 to wire 39. As in Fig. 1, transformers may be interposed between the light-responsive cell circuits and the corresponding lamps, and the effect of a relatively small resistance change may be increased by means of VVheatstone bridge or potentiometer connections.

The coil 10 of electro-responsive device E is connected in multiple with lamp Y of signal S by means of wires 46 and 47.

As shown in Fig. 2, section AB is occupied by a car or train TV, so that the armature of electro-responsive device EB occupies its intermediate position, wherein both of the light-responsive cells 13 and 13 controlled by this electro-responsive device, are dark. The circuit for lamp G of signal S is then of such high resistance that this lamp is extinguished. The connection between the terminals of the secondary 15 of transformer T is likewise of such high resistance that the voltage across lamp It of signal S is suflicient to cause this lamp to be lighted. Lamp Y of signal B is extinguished for reasons which will appear hereinafter.

Under this condition, that is, when electro-responsive device E is ole-energized, the voltage across the right-hand half of secondary 15 of transformer T is comparatively high, so that lamp Y of signal S is lighted, and the coil 10 on the armature of electro-responsive device E creates a stronger torque than the coil 9 on the same armature. The armature of the latter device is therefore swung to the right, so that the light-responsive cell 13 at signal S is illuminated. This causes the shunt around lamp G to be of low resistance, so that this lamp is extinguished, and the total resistance of the connection across the outside terminals of secondary 15 of transformer T is reduced to such value that lamp R of this signal is extinguished. It follows, therefore, that the lamp Y of this signal is the only one which is lighted, and so the signal indicates caution.

lVhen the armature of the electro-responsive device E occupies the position shown in the drawing, the potential across lamp Y of signal S is comparatively low, so that this lamp is extinguished and the armature of electro-responsive device E is swung to the left, in which position the light-responsive cell 13 is illuminated. This reduces the resistance of the circuit for lamp G in signal S to such value that this lamp becomes lighted. The resistance of the connection across the outside terminals of secondary 15 of transformer T is also reduced to such value that lamp It is extinguished. It follows, therefore, that signal S indicates proceed, that is, lamp G of this signal is lighted.

The foregoing operation of F 2, of course, requires the proper proporti'oning of resistance 31, 32, 33 and 4:2, as well as the proper resistances for lamps R, Y and Gr, and for the light-responsive cells 13 and 13 It will be obvious, however, to those skilled in the art that these parts can be so proportioned that the apparatus will operate in the manner set forth.

Referring now to Fig. 3, the operation of the electro-responsive device E is the same as in Fig. 1, but the control of the signals by these devices is somewhat different. Two light-responsive cells are provided for each signal and are designated 13 and 13*, respectively. When the armature of any device E is in its intermediate position, a beam of light is thrown on the corresponding light-responsive cell 13 and when the armature is in the left-hand extreme position a beam of light is thrown on the corresponding cell 13 When the armature is in the right-hand extreme position, it does not throw a beam of light on any light-re sponsive cell.

Referring specifically to signal S", the circuit for the proceed lamp G is from the right-hand terminal of secondary 15 of transformer T through wires 49 and 50, lamp G, cell 13 and wire 51 to the left-hand terminal of secondary 15. The stop or red lamp of this signal is connected in series with the caution or yellow lamp Yof signal S the circuit being from the right-hand terminal of secondary 15 of transformer T through wires 49 and 52, lamp Y. of signal S wire 53, lamp R of signal S cell 13 and wires 54 and 51 to the left-hand terminal of secondary 15. In each of these circuits the light-responsive cell may be placed in the primary circuit of a transformer, the secondary of which supplies the current to the lamp.

As shown .in the drawing, track section AB is occupied by a car or train W, so that the electro-responsive device E is deenergized, and the cell 13 for signal S is consequently illuminated. Lamp R for this signal and lamp Y for signal S are therefore lighted, but lamp G of signal S is dark because of the high resistance of the circuit for this lamp. Signal S therefore indicates stop. As for signal S both of the light-responsive cells are dark, so that moth lamps G and R of this signal are extinguished. Lamp Y being lighted, the signal indicates caution. Referring to signal S the lightresponsive device 13 is illuminated, so that the proceed lamp G is lighted. Lamp Y is extinguished because lamp R for the signal next in advance is extinguished. Lamp R for signal S is extinguished, because the cell 13*, which controls this lamp, is dark.

The operation of the system shown in Fig. 3 will be understood from the foregoing without further discussion.

Referring now to Fig. 4, the apparatus shown herein 1s the same as that shown in Fig. 1, with the exception of the means for energizing armature coil 10 of the electroresponsive devices E. In Fig. 4 this coil is supplied with current from the track circuit of the section next in advance through the medium of a transformer designated by the reference character H with a suitable exponent. As in Fig. 1, transformers may be introduced between the light-responsive cells and the lamps.

The torque due to the armature coil 9 of each electro-responsive device E tends to swing the armature to the right, whereas the torque due to coil 10 tends to swing the armature to the left. When the track circuits, by which these coils are supplied with current, are not influenced by trains, the torque due to coil 10 exceeds that due to coil 9 so that the armature is swung to the left. When, however, the supply of current to coil 10 is discontinued but the supply to coil 9 is not interrupted, the armature swings to the right. 7

As shown in the drawing, track section AB is occupied by a car or train W, so that the field coils 8 and 8 as well as the armature coil 9, of the electro-responsive device E are de-energized. The armature of this device occupies its intermediate position, therefore, so that signal S indicates stop.

Considering the electro-responsive device E the supply of current to armature coil 1,0 is discontinued, owing to the presence of the car or train in section AB, but the remaining coils of this device are energized so that the armature is swung to the right and signal S indicates caution. As for the electro-responsive device FP, it will be seen that both armature coils are energized, but inasmuch as the influence of coil 10 exceeds that of coil 9, the armature .ofthis device is swung to the left, so that signal S indicates proceed.

Referring now to Fig. 5, I have here shown an electro-responsive device Q of the induction motor type, which may be substituted for the galvanometer type of device E shown in each of the preceding views. The induction motor device Q comprises a shell type of rotor 75, together with the two usual stator windings 71 and 72 spaced 90 apart, the phases of the currents in these windings being displaced to the proper extent by a reactance 7 3 in series with winding 7 2. The two windings 71 and 72 are connected in multiple across the rails of track section B C so that when this section is unoccupied torque will be exerted on the rotor 75 tending to turn it in one direction. The de vice is provided with a third stator winding 74, which is spaced 180 from winding 71, and which contains a larger number of turns than winding 71. Winding 74 is supplied -with current from transformer H which in turn receives current from the track circuit for track section A-B. Mirror 11 is operatively connected withthe rotor 5.

hen track section 13-0 is occupied by a car or train, such as W, both windings 71 and 72 are de-energized, so that rotor 75 assumes a middle position to which it is biased by suitable means. When train W passes into section AB, current is supplied to windings 71 and 72, but not to winding 74, whereupon rotor 75 is swung in one direction, such as to the right. As the train passes out of section A--B, current is again supplied to winding 74 and, the torque exerted by this winding being in the opposite direction to that due to winding 71, the rotor 75 is swung in the other direction, which in this instance would be to the left. course, understood that the mirror 11 will be employed to control one or more light-responsive cells, such as the cells 13 shown in Figs. 1 to 4, inclusive.

Referring now to Fig. 6, I have here shown one form and arrangement of mirrors and light responsive cells, together with one means for controlling the mirrors by the electro-responsive device. The parts are en-' It is, of 7 til device E is located in the compartment 77, while compartment 7 8 contains the optical portion of the apparatus. The two field coils 8 and 8* of the electro-responsive device E are mounted in fixed position by a suitable means which are not shown in the drawing, it being understood that one of these coils is directly behind the other in Fig. 6. The armature coils 9 and 10 are mounted on a shaft 80, which is supported in suitable bearings in the case 7 6, and which shaft passes through an opening in the partition 79. Attached to the shaft 80 are two mirrors 11 and 11 which are arranged to project rays of light from the lamp 12 to the cells 13 and 70, respectively. It is, of course, understood that the three cells 13 13 and 13 of Fig. l, for example, are located one behind the other in Fig. 6. When polarity controlling cells are employed, as for example the cells 70* and TO of application by Grondahl and Howard, Serial No. 161,750, filed on even date herewith, these cells will likewise be located one behind the other in Fig. 6. The lamp 12 is mounted in a tube 81 which is preferably provided with a door near the lower end. The lamp is arranged to slide lengthwise in this tube from the position shown in the drawing, which is the operative position, to a position opposite the door where it may be readily reached for inspection and renewal.

Referring now to Fig. 7, the structure shown therein is the same as that of Fig. 6, except that the shaft 80 is suspended by two phosphor bronze straps 82, 82, which are anchored at the top of the casing 76, thus eliminating the bearings and so increasing the safety factor of the device. It is, of course, understood that the shaft 80 in both Figs. 6 and 7 is biased to an intermediate position by suitable means which are not shown in these views.

It may be that in actual practice the use of mirrors will be undesirable on account of the diiliculty of keeping the reflecting surfaces in polished condition. If this is so, then apparatus of the type shown in Figs. 8 and 9 may be employed. Referring to these views, the apparatus comprises an electroresponsive device Q of the induction motor type, which device is shown diagrammatically in Fig. 5. The rotor is of the shell type, and is fixed to a shaft 89 which is Journaled in suitable bearings in the compartment 77 of casing 76. Located in the compartment 78 is a drum 90 which is attached to shaft 89, and which, consequently, is oscillated by the rotor 75. This drum 90 is provided with three openings 90, 90 and 90, and the lamp 12 is located in the axial line of the drum. The three signal controlling light-responsivecells 13 13 and 13 are mounted in fixed position in the compartment 78 and are preferably located in pockets as indicated in Fig. 9. The polechanging cells 70, when such are employed, are similarly mounted in the same compartment. The parts are so arranged that when the rotor 75 occupies its intermediate position the opening 90 registers with cell 13 and that when the rotor is swung in one direction or the other to an extreme position this opening registers with cell 13 or 13 The other two openings in the drum are so arranged that opening 90 registers with cell 70 when the rotor is in its intermediate position, and that opening 9O or 90 registers with cell 7O when the rotor occupies one extreme position or the other.

The rotor 75 is biased to the intermediate position by a suitable means, such as counterweight devices 91. The lamp 112 is mounted in a tube 81 and passes through a large opening 90 in the bottom of the drum 90.

It will, of course, be apparent that an electro-responsive device; of the galvanometer type, such as that shown in Fig. 6, may be substituted for the induction motor type shown in Fig. 8, and that, similarly, the optical apparatus of Figs. 6 and 7 maybe actuated by an induction motor type of electro-responsive device, such as that shown in Fig. 8.

Although I have herein shown and described only certain forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination, a track circuit coniprising track rails, a source of current and an electro-responsive device; a lamp, a lightresponsive cell, means controlled by said device for illuminating said cell from said lamp, and a signal controlled by said lightresponsive cell.

2. In combination, a track circuit comprising track rails, a source of current and an electro-responsive device; a lamp, a lightresponsive cell, means controlled by said device for illuminating said cell from said lamp when said track circuit is not occupied, and a signal controlled by said cell and arranged to give a proceed indication when the cell receives rays from said lamp but not at other times. i

3. In combination, a track circuit comprising track rails, a source of current and an illuminating said cell from said lamp, and

a signal controlled by said light-responsive cell, 7

4:. A railway signaling system comprising a series of track sections; a track circuit for each section including the track rails of the section, a source of current and an electroresponsive device; a lamp foreach section, a first and a'second light-responsive cell for each section, means controlled by each elec tro-responsive device for throwing rays from the corresponding lamp to the corresponding first light-responsive cell when the corresponding section is unoccupied but not when such section is occupied, means associated with each section and operating when the section is occupied to cause the electroresponsive device for the section next in the rear to throw light rays from its lamp to the second light-responsive cell; and a signal for each section controlled by said lightresponsive cells and arranged to indicate proceed when the first cell is illuminated, caution when the second cell is illuminated, and stop when neither cell is illuminated.

5. A railway signaling system comprising a series of track sections, a lamp and three light responsive cells for each section; means for throwing rays from the lamp for each section on the first cell for such section when the section is occupied, on the second 1 cell for such section when the section is unoccupied and the section next in advance is occupied, and on the third cell "for the section when such section and the section next in advance are unoccupied; and a signal for each section controlled by said cells and arranged to indicate stop when the first cell is illuminated, caution when the second cell is illuminated, and proceed when the third cell is illuminated. 6. Railway trafiic controlling apparatus comprising a light-responsive cell, a lamp, means including a movable member governed by the passage of cars or trains for controlling the supply oflight from said lamp to said cell, and trafiic governing means controlled by said cell.

7. A railway signaling system comprising a series of track sections, a lamp and three light-responsive cells for each section, a source of current connected with the rails of each section; an electro-responsive device for each section receiving current from the rails of the section and from the rails of the section next in advance, said device having a member which occupies one position when the corresponding section and the section next in advance are unoccupied, a second position when the corresponding section is unoccupied and the section next in advance is occupied, and a third position when the corresponding section is occupied; means controlled by each member for illuminating the first, second or third corresponding light-responsive cell from' said lamp according to the position occupied by said member; and signals for the sections controlled by said light-responsive cells.

8. In combination, a section of railway track, a track circuit for such section including a source of current and an electro-responsive device, a light-responsive cell, means controlled by said device for illuminating said cell when the device is in one condition, and a signal controlled by said cell.

9. In combination, a section of railway track, a track circuit for such section including a source of current and an electroresponsive device, a light-responsive cell, means controlled by said device for illuminating said cell when the track section is unoccupied but not when it is occupied, and a signal controlled by said cell.

10. Railway. trafiic controlling apparatus comprising a light-responsive cell, a movable member governed by the passage of cars or trains, means controlled by said member for at times supplying light to said cell, and traflic governing means controlled by said cell.

11. Railway traffic controlling apparatus comprising a track circuit including an electro-responsive device having a movable member, a light-responsive cell, means con trolled by said member for supplying light to said cell, and traliic governing means controlled by said cell.

12. In combination, a section of railway track, a lamp and a light-responsive cell "for said section, a movable mirror controlled by the presence and absence of trains on said section for at times reflecting light from said lamp to said cell, and a signal c0ntrolled by said cell.

18. Railway traflic controlling apparatus comprising a movable member governed by the passage of cars or trains, a lamp, a lightresponsive cell, a mirror operatively con nected with said movable member for at times reflecting light from said lamp to said cell, and traffic governing means controlled by said cell.

14:. In combination, a railway track divided into sections, a lamp and a plurality of light-responsive cells for each section, means controlled by traflic conditions in each section and in advance of such section for selectively lighting the cells for the section from the associated lamp, and tralfic governing means for the sections controlled by said cells.

15. In combination, a railway track divided into sections, a lamp and a plurality of light-responsive cells for each section,

means controlled by trafiic conditions in each section and in advance of such sec tion for selectively lighting the cells for the section from the associated lamp, and signals controlled by said cells and adapted to indicate stop, caution and proceed.

16. Railway traflic controlling apparatus comprising a series of track sections, an electro-responsive device for each section having a movable member controlled by trafiic conditions in its own section and in the section next in advance, a plurality of light-responsive cells for each section, means controlled by each movable member for se lectively lighting the associated cells, and traiiic governing means controlled by said cells.

17. Railway traflic controlling apparatus comprising a series of track sections, a lamp and three light-responsive cells for each section, means for each section for causing light from the lamp for such section to fall on the first of the associated cells when the section is occupied, on the second of the associated cells when the section is unoccupied and the next section in advance is occupied, and on the third of the associated cells when the section and the next section in advance are unoccupied; and traiiic governing means for the sections controlled by said cells.

18. Railway trafiic controlling apparatus comprising a series of track sections, a lamp and three light-responsive cells for each section, means for each section for causing light from the lamp for such section to :tall on. the first of the associated cells when the section is occupied, on the second of the associated cells when the section is unoccupied and the next section in advance is occupied, and on the third of the associated cells when the section and the neXt section in advance are unoccupied; and a signal for each section controlled by the associated cells and indicating stop, caution or clear according as the first, second or third of said cells is lighted.

19. The method of controlling railway traffic which consists in throwing light from a lamp upon one or another of a plurality of light-responsive cells according to the conditions of traffic, and controlling a traffic governing device in accordance with the lighting of said cells.

20. The method of controlling railway trafiic which consists in operating a movable member in accordance with traffic conditions, lighting one or another of a plurality of light-responsive cells from a lamp according to the position of said member, and controlling a traiiic governing device in accordance with the lighting of said cells.

21. The method of controlling railway traffic which consists in operating a movable member in accordance with traflic conditions, throwing light from a lamp to a light-responsive cell when said member is in one position but not when it is in another position, and controlling a traffic governing device by said cells.

In testimony whereof I aflix my signature.

LARS O. GRONDAHL. 

